Not showing available RAM

This answer has been mainly provided by jawtheshark in the comments. I am going to summarize it here to close the issue. The problem is that Linux takes, for integrated GPU's, a part of the RAM and uses it as VRAM. The graphics part of the APU reserves 4GB of the system RAM for its use. Looking at this kernel documentation: kernel.org/doc/html/latest/gpu/amdgpu.html The parameter: vramlimit (int) --> Restrict the total amount of VRAM in MiB for testing. The default is 0 (Use full VRAM). Which means that the 'auto' option for delegating RAM to the integrated GPU, delegates a large amount of RAM to the GPU. Since I only use the machine as a workstation, I will set the 'auto' option in bios to '1 GB', the minimum.